Method for producing watersoluble leuco vat dyestuff



Patented July 19, 1949 UNITED ifi OFFICE METHOD FOR PRODUCING WATER- SOLUBLE LEUCO VAT DYESTUFF No Drawing. Application June 3, 1944, Serial No. 538,693

4 Qlaims.

This invention relates to the dyeing of textile materials and relates more particularly to the dyeing of cellulose acetate or other organic derivative of cellulose textile materials with vat dye stuffs.

An object of this invention is the production of water-soluble leuco vat dyestufis Which may be applied to textile materials from aqueous solutions free of alkaline materials.

Another object of this invention is the provision of an improved process for the coloration of cel lulose acetate or other organic derivative of cellulose textile materials with vat dyestuffs.

A further object of this invention is the application of vat dyestufis of leuco form to cellulose acetate or other organic derivative of cellulose textile materials from aqueous solutions free of alkali.

Other objects of this invention will appear from the following detailed description.

The application of Vat colors to cellulose acetate or other organic derivative of cellulose materials may be effected by applying the vat dyestuffs to the materials in reduced or leuco form employing an alkaline vat, and then oxidizing the reduced dyestufi on the material back to the colored form. some vat dyestufis may also be employed by applying the dyestufis, in an unreduced but dispersed form, to the textile material being dyed, by padding or other operations. In general, the above processes have ofiered the only really practical methods whereby the vat dyestuffs may be utilized. The application of leuco dyestuffs from the reduced vat has a very distinct disadvantage however when dyeing cellulose ester materials. Due to the strongly alkaline nature of the vat, there is a pronounced tendency for the alkaline vat to effect at least a partial saponification of the cellulose ester materials. Such saponification is quite disadvantageous since it tends to weaken the cellulose ester textile material. Moreover, saponification of cellulose ester materials alters the hand, appearance and dyeing properties of said materials.

We have now discovered, however, that the vat dyestufis may satisfactorily color textile materials having a basis of cellulose acetate, or other organic derivative of cellulose, by a novel method in which the vat dyestufis, in reduced or leuco form, may be applied from aqueous solutions free of alkaline reducing agents. In accordance with the process of our invention, the dyestufis, after being vatted and reduced to the leuco form, are precipitated from the vat by the addition thereto of a non-solvent organic liquid, preferably ethyl alcohol. The precipitate obtained is dissolved in water and the aqueous solution thus produced is applied to the cellulose acetate materials by the usual dyeing methods. When the leuco vat dyestuff which is applied to the materials in this way is oxidized, fabrics and other cellulose acetate textile materials dyed in clear bright shades are obtained. The dyed materials possess excellent washing, light and acid-fading resistance.

The reduction of the vat dyestufi is effected in he usual way, i. e. by the use of a reducing agent comprising sodium hydroxide and an alkaline hydrosulfite, such as sodium hydrosulfite. Usu ally from 50 to 1000 parts by weight of sodium hydroxide and 70 to 1400 parts by weight of sodium hydrosulfite are employed when vetting 100 to 2000 parts by Weight of vat dyestuh. The

vatting is efiected in aqueous solution at temperatures of to F.

Any suitable non-solvent for the vatted, leuco dyestuff may be employed for precipitating said reduced dyestufi from the vat. Non-solvents such as isopropyl alcohol or methyl alcohol may be employed but optimum results are achieved by the use of ethyl alcohol as precipitant. The nonsolvent is added to the vat until the leuco dyestufi in solution precipitates.

After precipitation, the leuco ivat dyestufi is dissolved in water and the resulting bath is applied to the cellulose acetate or other organic derivative of cellulose textile material by any suitable method of application. Among the methods which may be employed, are, for example, padding, jig dyeing or winch dyeing. Our novel method of dyeing may also be employed when dyeing staple fibers and when dyeing continuous filament yarns in package form.

The dyed textile material is washed after dyeing, and the leuco vat ,dyestuff is then oxidized back to the colored form. oxidizing agents such as sodium perborate or hydrogen peroxide may be employed, but we prefer to employ as the oxidizing agent sodium bichromate in aqueous solu-- tion in a concentration of 0.5 to 1.0%. After oxidation the dyed material is washed, soaped, dried and finished.

Since, in accordance with our investigation, the vat dyestufis are applied without any necessity for entering the cellulose ester materials in an alkaline vat, there is no danger whatever of undesirable saponification or other deleterious action on the cellulose ester material. The colors obtained exhibit excellent fastness to light, acidfading and washing.

In order further to illustrate our invention but without being limited thereto the following examples are given:

Example I 500 parts by weight of Calcosol Red BN (Color Index No, 1162) double paste are reduced at 140 F. with a vat containing 250 parts by weight of sodium hydroxide and 350 parts by weight of sodium hydrosulphite dissolved in 5000 parts by weight of water. About 8000 parts by weight of ethyl alcohol (90 by weight) are added to the reduced vat and a bordeaux precipitate forms rapidly. The precipitate is filtered from the vat and is dissolved in 10,000 parts by weight of water at a temperature of 120 F. The desired dyebath is formed by adding the above aqueous solution of the precipitated dyestufi to 50 times its weight of water. A cellulose acetate fabric is dyed on a jig at 120 F. employing the dyebath and the fabric is dyed for two hours. When dyeing is completed, the fabric, now colored a yellow shade, is washed. The leuco dyestuff on the fabric is then oxidized in a 0.5% aqueous solution of sodium bichromate at 100 F. During oxidation, the fabric goes through a blue red shade and finally comes to the final shade which is a rose pink. The dyed fabric is then washed, soaped and finished and is found to be fast to light, washing and acid-fading.

Example II 500 parts by weight of Indanthrene Brilliant Green B paste are reduced at 140 F. with a vat containing 250 parts by weight of sodium hydroxide and 350 parts by weight of sodium hydrosulphite dissolved in 5000 parts of water. About 8000 parts by weight of ethyl alcohol (90% by weight) are added to the reduced vat and a reddish orange precipitate forms rapidly. The precipitate is filtered from the vat and is dissolved in 10,000 parts by weight of water at a temperature of 140 F. The desired dyebath is formed by adding the above aqueous solution of the precipitated dyestuif to 50 times its weight of water. A cellulose acetate fabric is dyed on a jig at 140 F. employing the dyebath and the fabric is dyed for two hours. When dyeing is completed, the fabric, now colored a reddish orange shade, is washed. The leuco dyestuff on the fabric is then oxidized in a 0.5% aqueous solution of sodium bichromate at 100 F. During oxidation, the fabric goes through a blue shade and finally comes to the final shade which is a green. The dyed fabric is then washed, soaped and finished and is found to be fast to light, washing and acid-fading.

Any suitable vat dyestuif may be employed in the dyeing process of our invention for dyeing cellulose acetate or other organic derivative of cellulose. Examples of other organic derivatives of cellulose which may be dyed by our novel process are cellulose esters such as cellulose propionate, cellulose butyrate, mixed esters such as cellulose aceto-propionate and cellulose acetobutyrate and cellulose ethers such as ethyl cellulose and benzyl cellulose.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the production of leuco vat dyestuffs capable of dyeing from substantially neu-l tral aqueous solution, which comprises reducing a vat dyestuff to the leuco form in an alkaline i vat, and adding an organic liquid non-solvent for said leuco dyestuif to said vat so as to cause said leuco vat dyestuff to precipitate from the vat in which it is reduced in the form of a watersoluble leuco vat dyestuif.

2. Process for the production of leuco vat dyestuffs capable of dyeing from substantially neutral aqueous solution, which comprises reducing a vat dyestuif to the leuco form in an alkaline vat, and adding a water-miscible non-solvent for said leuco dyestuif to said vat so as to cause said leuco vat dyestufi to precipitate from the vat in which it is reduced in the form of a watersoluble leuco vat dyestufif.

3. Process for the production of leuco vat dyestuffs capable of dyeing from substantially neutral aqueous solution, which comprises reducing a vat dyestuff to the leuco form in an alkaline vat, and adding a lower aliphatic alcohol to said vat so as to cause said leuco vat dyestuii" to precipitate from the vat in which it is reduced in the form of a water-soluble leuco vat dyestuff.

4. Process for the production of leuco vat dyestuffs capable of dyeing from substantially neutral aqueous solution, which comprises reducing a vat dyestufl to the leuco form in an alkaline vat, and adding ethyl alcohol to said vat so as to cause said leuco vat dyestuff to precipitate from the vat in which it is reduced in the form of a water=soluble leuco vat dyestuif.

CYRIL M. CROFT. WALTER H. HINDLE.

REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS Number Name Date 472,267 Michaelis Apr. 5, 1896 833,654 Wimmer Oct. 16, 1906 999,055 Oberreit July 25, 1911 1,247,927 Brochet Nov. 27, 1917 1,546,969 Clavel July 21, 1925 1,771,763 Bauder July 29, 1930 1,803,219 Tagliani Apr. 28, 1931 1,900,172 Ellis Mar. 7, 1933 2,035,362 Bauer Mar. 24, 1936 2,044,796 Krause June 23, 1936 2,063,594 Fairweather et a1. Dec. 8, 1936 2,107,526 Dreyfus Feb. 8, 1938 2,136,428 Fox Nov, 15, 1938 2,174,372 Zahn Sept. 2r, 1939 2,132,963 Dreyfus Dec. 12, 1939 FOREIGN PATENTS Number Country Date 506,203 Great Britain May 24, 1939 552,619 Great Britain Apr. 16, 1943 OTHER REFERENCES McArdle, Solvents in Synthetic Organic Chemistry, pp. 151-2, pub. by D. Van Nostrand Co. 1925 edition.

Certificate of Correction Patent No. 2,476,287 July 19, 1949 CYRIL M. CROFT ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 47, for the word investigation read invention; column 3, line 10, for 90 read 90%;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 17th day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant G'ommissioner of Patents. 

